I'm going to say something that most will frown upon: You can also remove the aperture lever so it works in AV mode. Aperture must then be set by the aperture ring. And the use of green button is then no longer needed. You can then just shoot away at any aperture. Well, at F22 the viewfinder will be quite dark though.
And about focussing with the stock screen, I don't have many problems with that. I use a Porst 55 f1.2, with an even thinner DOF at f1.2. True, sometimes I use liveview to help out a little. But at f1.2 the viewfinder is extremely bright, that I would even say that it even gets easier a little.
A rear-mounted TC eats light. A screw-on front adapter doesn't. This is similar to using a Raynox close-up adapter versus macro tubes. The extension eats light, the Raynox doesn't. The cost of using any add-on optics is some slight loss of contrast and saturation, which can be tweaked in PP / RAW development or in-camera. With close-up and wide adapters, and cheap tele adapters, there is also some loss in edge acuity, but I haven't seen that with good tele adapters.
Brands to look for include Sony, Olympus, Canon, Kowa, Quantaray|Sigma, Vivitar, Minolta, Sankyo, Promaster|Tamron, Kenko -- NOT Phoenix, Star-D, Tiffen, no-names. Ambico may be OK but I'm not sure. Here is where I search for them. Like I said, stick to name brands. Plug in 1.4x or 1.7x as well as 1.5x for searching. Many of these are for camcorders -- avoid those with rear threads under 46mm. I use a Sony VCL-1546A, which means 1.5x on a 46mm thread, and I use it (via step rings) on lenses with 49mm or 52mm threads, with no vignetting. It cost me US$4 shipped. My Kowa 1.75x was one buck less. I have no complaints.